The primary purpose of this research is a study of the replication of the negative-stranded RNA viruses in cell culture using vesicular stomatitis (VSV) as a prototype. The primary objectives of the research will be to study the mechanism by which the single negative strand of RNA replicates and to study how the process of RNA replication may be regulated. Specific goals will be: 1. To determine if a complete strand of RNA complementary to virion RNA is the template for replication of progeny RNA. 2. To characterize the molecular nature and intracellular form of this RNA. 3. To determine whether the synthesis of progeny virion RNA occurs via a double or partially double stranded replicative intermediate and to characterize this structure. 4. To determine if a replicative intermediate structure is the immediate precursor of virion RNA. 5. To characterize the requirement for protein synthesis in replication. 6. To identify viral specific proteins involved in the replication process and in its regulation and study their function. A key factor in the study will be the use of viral mutants temperature sensitive for RNA transcription so that RNA replication can be examined in a situation where it is the predominant event.